Can I have the same item but new?
'Nuovo' — NWO-vo. The 'uo' is a diphthong — say it smoothly.
Use when you want an identical replacement rather than a different product. Adding 'ma nuovo' clarifies you expect an unopened item, not the display model or another returned item.
'Lo stesso' means the same (masculine). 'Ma nuovo' (but new) is a short contrast clause. This phrase is direct and clear. Adding 'per favore' at the end maintains courtesy: 'Posso avere lo stesso articolo ma nuovo, per favore?'
Vorrei la stessa cosa ma in buone condizioni.
I would like the same thing but in good condition.
Implies the original was not in good condition.
Avete lo stesso modello non aperto?
Do you have the same model unopened?
Explicitly asks for sealed stock.
Non voglio il modello esposto.
I don't want the display model.
Refuses display unit tactfully.
In Italy, asking to check a replacement item in the shop before leaving is perfectly normal and accepted. It avoids another return trip. Staff generally welcome this as it prevents a second return.